The upload-artifact action was changed from the upstream GitHub version to
christopherhx/gitea-upload-artifact@v4 to ensure compatibility with the
Gitea CI runner environment.
Remove the old .github/workflows/.githubCI.yml that used v2 actions and a single .travis.sh build script for Linux, macOS, and Windows. Add a new .gitea/workflows/ci.yml that builds only on Linux using the wren_cli.make makefile with a matrix of release_64bit and debug_64bit configs, runs Python-based tests with a _d suffix for debug builds, and uploads artifacts named wren-cli-linux-<config>.
